Microstructure evolution of a W-doped ZrB2 ceramic upon high-temperature oxidation

This basic research deals with the microstructure evolution of a W-doped ZrB2 ceramic, as-sintered and upon oxidation at 1650 degrees C. Transmission electron microscopy enabled to disclose microstructural features occurred during oxidation never observed before. In the pristine material, (Zr,W)B-2 solid solutions surround the original ZrB2 nuclei, whereas refractory W-compounds at triple junctions and clean grain boundaries are distinctive of this ceramic. After oxidation, the microstructure is typified by intragranular nanostructures, in which nanosized W inclusions remained trapped within ZrO2 grains, or decorate their surfaces. The understanding of the oxidation reactions occurring in the system as a function of the oxygen partial pressure was fundamental to conclude that W-based compounds do not notably suppress or retard the oxidation of ZrB2 ceramics.